On existing airplanes, the area located between the passenger floor, the airplane's skin and the floor struts is called “triangle”.
On existing airplanes, floor cross members, frames and struts are simple parts, assembled one to the other either rigidly, in particular by embedding, or flexibly using joints.
The portion of the frame located under the cargo cross member, called “fuselage tub frame” comprises a curved frame element and a cross member that serves as a mount for the cargo floor.
The upper portion of the frame comprises an upper curved frame element and a cross member under which the luggage bins are fastened.
Joining these members together is realized by means of screws, rivets or other means of fastening.
Assembling these elements with each other requires much time because of the large number of fasteners that have to be installed, in particular between the floor cross member and the upper frame.
In particular the cross member/frame junction must be realized in an area where the forces to be transmitted are relatively large, i.e. for which the embedding torque is large. To achieve this, the heights of the frames and cross members are increased locally to make it possible to locate all the fasteners required for the junction.
To reduce the manufacturing cost of the member parts and simplify the definition of the parts that are in contact, the frames may be realized with extruded sections, machined members, folded members or members assembled together to form the frame elements such as frames.
It is not possible in general to keep a constant height at the junction with the cross members because of the large number of fasteners to be installed. Because of this, the cost of the simple part is increased.
Document FR 2 877 916 A1 describes a particular realization for which an upper frame comprises link arms to a floor cross member and to a lower frame.
However, for large aircrafts, such an upper frame is cumbersome and complex to realize.